Method for repairing and lustering defects on hydrophilic coat surface

ABSTRACT

A method for repairing and lustering defects on a hydrophilic coat surface is reported. The method comprises the steps of applying a buffing composition on a hydrophilic coat surface; and buffing the hydrophilic coat surface to which the buffing composition has been applied. The buffing composition is an aqueous composition which comprises water and a water-soluble high-boiling-point liquid organic compound, and further comprises either a combination of abrasive particles and a dispersant, or lustering agent, or the both. The method allows for the removal of defects on a hydrophilic coat surface with good finish after repairing and without deteriorizing the antifouling function of the hydrophilic coat against urban fouling substances.

FIELD

The present invention relates to a method for repairing and lusteringdefects on a hydrophilic coat surface and, in particular, to a methodfor repairing and lustering defects on a hydrophilic coat surface thatrequires a very fine finish, such as an automobile coat surface.

BACKGROUND

Painting is generally performed on an automobile surface for the purposeof imparting surface protection, desired colors, and aestheticappearance. Painting is an operation to spread a paint (i.e., is a resincomposition) over the surface of an automobile body and to harden thepaint to form a continuous resin-coated film having an approximatelyuniform thickness. The resin-coated film formed on the surface of anobject by painting is called a coat.

If some functional hindrance of the paint (e.g., foaming, adhesion ofdust, or the like) occurs during the painting step, the uniformity,continuity, or the surface flatness of the coat to be formed isinhibited, and defects such as haze marks, recesses, and wounds may begenerated on the coat surface. Defects are also generated on the coatsurface when the uniformity, the continuity, or the surface flatness ofthe coat is altered by friction or collision of the automobile bodyafter the coat is formed. If the defects are present on the coatsurface, the aesthetic appearance of the automobile body isdeteriorated, and the value of the automobile is decreased. For thisreason, defects on the coat surface must be repaired and polished.

Japanese Patent Laid-open Publication No. 02-269791 discloses a methodfor repairing the defects on the coat surface. According to this method,the defects of the coat are removed by first sanding with a very finegrade polishing material. Next, the trace of the removed defects isbuffed using a buffing composition to remove the scratches produced bythe sanding step. Finally, the residual buffing composition is removedusing a cotton cloth, thereby producing a uniform, glossy finish. Onesuitable buffing composition for use in this method is commerciallyavailable under the trade designation “FINESSE-IT” from Minnesota Miningand Manufacturing Company.

Various functional paints have been developed in recent years, and acoat is known which exhibits an excellent antifouling property againstfouling substances specific to urban areas (e.g., smoke and exhaustgas). For example, “Painting Technology”, Vol. 31, No. 7 (1996), pp.268-273 explains a mechanism of the antifouling function exhibited bysuch a low-fouling type coat against urban fouling substances. Since thelow-fouling type coat has a high surface energy and shows a hydrophilicand oil-repellent property, oleophilic fouling substances (e.g., smokeand exhaust gas) are unlikely to adhere to the coat and, if they adhere,are easily washed away by rain or the like.

When defects are generated on the surface of the low-fouling type coatand if an attempt is made to repair the defects by a conventionalmethod, problems arise such as insufficient removal of the defects, poorfinish after repairing, and deterioration of the antifouling property ofthe coat against urban fouling substances after repairing. Theseproblems are raised because oleophilic ingredients (e.g., aliphatichydrocarbon and petroleum-based solvents) are contained in the buffingcomposition used in the step of buffing the coat surface. Theseoleophilic ingredients are not compatible with the hydrophilic coat andhave an insufficient polish promoting function. Once the oleophilicingredients penetrate into the hydrophilic coat they cannot be easilyremoved, so that the hydrophilic and oil-repellent function isdeteriorated on a portion of the coat surface where the oleophilicingredients have penetrated. On the other hand, if the oleophilicingredients are removed from the buffing composition, removal of thedefects by the buffing step will be insufficient, thereby giving a poorfinish after repairing

SUMMARY

The present invention provides a method for repairing and lusteringdefects on a coat surface, by which method the defects on a hydrophiliccoat surface is sufficiently removed with good finish after repairing,and the antifouling function of the hydrophilic coat against urbanfouling substances is not deteriorated. The method of the presentinvention comprisies the steps of applying a buffing composition on ahydrophilic coat surface; and buffing the hydrophilic coat surface towhich the buffing composition has been applied, wherein said buffingcomposition is an aqueous composition which comprises water and awater-soluble high-boiling-point liquid organic compound, and furthercontains either a combination of abrasive particles and a dispersant, alustering agent, or both.

DETAILED DESCRIPTION

The buffing composition for use with the method of the present inventionis an aqueous composition containing water and a water-solublehigh-boiling-point liquid organic compound, and further containingeither a combination of abrasive particles and a dispersant, a lusteringagent, or both.

Water-Soluble High-Boiling-Point Liquid Organic Compound:

Preferred water-soluble high-boiling-point liquid organic compounds, arethose that are effective in swelling and softening the hydrophilic coat.Softening the hydrophilic coat improves the polishing performance of thebuffing composition.

The hydrophilic coat may be generally an acrylic melamine resin, anaminoalkyd resin, a urethane resin, or the like. The hardness of such acoat is generally H to 2H (JIS (1979, K5400)) before it is swollen withthe water-soluble high-boiling-point liquid organic compound. On theother hand, after it is swollen with the water-solublehigh-boiling-point liquid organic compound, the hardness of the coat ispreferably about B in view of promoting the polishing.

Since the buffing step is generally carried out for 1 to 5 minutes at anambient temperature of 25 to 60° C., the water-solublehigh-boiling-point liquid organic compound must be slightly volatile tosuch a degree that it is not dried during the buffing step. Accordingly,the water-soluble high-boiling-point liquid organic compound preferablyhas a boiling point of not less than 100° C., more preferably not lessthan 130° C.

The water-soluble high-boiling-point liquid organic compound preferablyhas a carbon number of 3 to 12, more preferably 3 to 6. If the carbonnumber is less than 3, the boiling point will be too low and it will bedried during the polishing step. If the carbon number exceeds 12, theability of the water-soluble high boiling-point liquid organic compoundto swell the coat will decrease.

Also, the water-soluble high-boiling-point liquid organic compound ispreferably one that can be easily washed away with water with littleremaining in the inside of the coat, even if it adheres to the coatsurface. Further, even if a small amount remains, it is preferably onethat does not give an adverse effect on the hydrophilic, oil-repellentfunction of the hydrophilic coat.

Preferable examples of water-soluble high-boiling-point liquid organiccompounds are polyhydric alcohols, hydroxyketones, and ether or esterderivatives of polyhydric alcohols. Specific examples include ethyleneglycol diglycidyl ether, ethylene glycol dimethyl ether, ethylene glycolmonoacetate, ethylene glycol monoethyl ether, ethylene glycol monobutylether, ethylene glycol monomethyl ether acetate, ethylene glycolmonomethoxymethyl ether, ethylene chlorohydrin, glycerol, diethyleneglycol diacetate, diethylene glycol dimethyl ether, diethylene glycolmonoethyl ether, diethylene glycol monoethyl ether acetate, diethyleneglycol monobutyl ether, diethylene glycol monomethyl ether, dipropyleneglycol monoethyl ether, dipropylene glycol monomethyl ether, triethyleneglycol monoethyl ether, triethylene glycol monomethyl ether, propyleneglycol monobutyl ether, diacetone alcohol, propylene glycol monomethylether, and others.

Among these, especially preferable water-soluble high-boiling-pointliquid organic compounds are diacetone alcohol and propylene glycolmonomethyl ether. These are excellent especially in the swellingproperty of the coat, and the polishing performance of the buffingcomposition.

The water-soluble high-boiling-point liquid organic compound istypically present in the buffing composition at 1 to 50 parts by weight,more preferably at 1 to 30 parts by weight, most preferably at 3 to 10parts by weight with respect to 100 parts by weight of water. If theblended amount of the water-soluble high-boiling-point liquid organiccompound is less than 1 part by weight, the coat will not swellsufficiently, failing to provide a polishing promoting effect, whereasif it exceeds 50 parts by weight, the coat will be too soft to provide agood finish on the coat surface after repairing.

Abrasive Particles:

Abrasive particles are a particulate material which provide a polishingeffect. They are preferably a hard material which has a good cuttingproperty and which does not give deep wounds easily on the polishedsurface when they are used as free abrasive particles. The averageparticle size of the abrasive particles is preferably from 10 nm to 100μm, more preferably from 1 to 10 μm. The particle size distributionshould be fairly narrow so that the buffing composition does not produceany undesired scratches.

The material of the abrasive particles is preferably aluminum oxide,silica, aluminum silicate, talc, kaolin, clay, or a mixture thereof.Especially preferable abrasive particles are alumina particles.

The abrasive particles are included in the buffing composition if abuffing function is desired. The content of the abrasive particles isnot more than 60 parts by weight, preferably 10 to 60 parts by weight,more preferably 20 to 40 parts by weight with respect to 100 parts byweight of water. If the abrasive particles are included in an amount of60 parts by weight, the polishing performance is not improved; and onthe contrary, the finish of the coat surface after repairing isdeteriorated.

Dispersant:

A dispersant is included in the buffing composition so that the abrasiveparticles do not agglomerate. Since the buffing composition of thepresent invention is an aqueous composition containing water, awater-soluble high-boiling-point liquid organic compound, abrasiveparticles, and other ingredients, the dispersant must perform thefunction of dispersing the abrasive particles, even in a water-alcoholmedium.

The dispersant may be generally a water-soluble surfactant. Specificexamples include polycarboxylic acids and salts thereof,polyaminoamides, and acid esters thereof.

The dispersant is included in the buffing composition preferably at anamount of 0.5 to 5 parts by weight with respect to 100 parts by weightof water. If the amount of the dispersant is less than 0.5 part byweight, the abrasive particles tend to agglomerate in the buffingcomposition, whereas if the dispersant is included in an amountexceeding 5 parts by weight, the dispersibility of the abrasiveparticles is not improved and they are likely to remain on the coatsurface after repairing.

Lustering Agent:

A lustering agent is included in the buffing composition so as to make afiner finish or to impart luster to the coat surface after repairing.This makes the repairing and lustering method of the present inventionalso suitable as a countermeasure against so-called hazing of the coatsurface. Since the lustering agent is a component that performs afunction of filling fine wounds by remaining on the coat surface afterrepairing, the lustering agent is preferably one that does not give anadverse effect on the hydrophilic oil-repellent function of thehydrophilic coat.

The lustering agent to be used may be a hydrophilic silicone or ahydrophilic wax. Specific examples include polyether denatured silicone,hydrophilic aminosilicone, hydrophilic epoxy silicone, glycerol,hydrogenated castor oil and derivatives thereof, amido compounds, andothers.

In particular, a hydrophilic aminosilicone composed of a block copolymerof polyether and amino denatured silicone is preferred because itremains on the coat surface or inside the coat and produces an effect ofmaintaining the luster and the hydrophilicity of the coat.

The amount of the lustering agent may be suitably adjusted in accordancewith the required finish of the coat surface after repairing. Generally,the lustering agent is allowed to be contained in the buffingcomposition in an amount of not more than 10 parts by weight, preferably0.5 to 10 parts by weight, with respect to 100 parts by weight of water.Even if the lustering agent is allowed to be contained at an amountexceeding 10 parts by weight, the finish of the coat surface afterrepairing is not significantly improved.

Other Additives:

Thickeners can be added to increase and adjust the viscosity of thebuffing compositions of the present invention. If the viscosity of thebuffing composition is too low, it tends to run down the verticalsurfaces of the automobile, and consequently, the operators cannotproperly buff with it. Therefore, thickeners are utilized to adjust theviscosity of the buffing composition.

Typical examples of thickeners include hydrous aluminum silicate, adimethyldioctadecyl salt of montmorillonite clay, an alkali-solubleacrylic polymer emulsion, colloidal silica, heavy metal soaps such aslead oleate, zinc oleate, zinc stearate, and aluminum stearate. Thepreferred thickener for use with the present invention is an aqueousalkali-soluble acrylic polymer emulsion.

Stabilizers and preservatives can be employed to inhibit bacterialgrowth in the buffing composition. Typical examples include methylparaben, ethyl paraben, propyl paraben, butyl paraben, potassiumsorbate, sorbic acid, and o-phenylphenol.

Pigments, dyes, and perfumes can also be added to the buffingcomposition of the invention as desired.

Preparation of Buffing Composition:

A buffing composition for use with the method of the present inventionis obtained by mixing the above-mentioned components with water. Thewater for use may be tap water, distilled water, or deionized water.Deionized water is preferred because the likelihood of bacterial growthis reduced due to the removal of ions and other minerals which maypromote microbial growth in the buffing composition.

The order of addition in preparing the buffing composition is, forexample, water, additives, a water-soluble high-boiling-point liquidorganic compound, a lustering agent, a dispersant, and abrasiveparticles. The mixture is continuously mixed as the various ingredientsare added. Thereafter, the buffing composition is mixed to form ahomogeneous dispersion with a high shear mixer.

Method for Repairing and Lustering Defects on a Hydrophilic CoatSurface:

According to the method of the present invention, surface defects arefirst discovered on the coat surface. The surface defects are, forexample, haze marks caused by poor hardening, pinholes caused by foamingin painting, abrasions caused by friction of an automobile body,adhesion of dusts, and scratches, hazing, and others remaining afterthese defects are removed in the sanding step. Then, the buffingcomposition is applied to the area on the hydrophilic coat surface wherethe surface defects are formed.

Next, the hydrophilic coat surface, to which the buffing composition hasbeen applied, is buffed. The buffing is generally performed in thefollowing manner. First, a buffing pad is secured to a buffing tool. Thepad and the buffing tool for use can be, for example, those manufacturedby Minnesota Mining and Manufacturing Company. Next, the buffing pad isplaced on the coat surface to which the buffing composition has beenapplied. The tool is turned on, and the coat surface is buffed aspressure is applied to the tool. The buffing period is typically 3 to 30seconds. The buffing may be performed several times as the pressure isincreased or decreased.

Thereafter, the buffing composition remaining on the polished surface isremoved by means of washing with water, wiping with woven cloth (e.g.,cotton cloth), nonwoven cloth, very fine fiber cloth of 0.1 to 0.5denier, or the like. An additional step of polishing the surface mayresult in an even finer finish.

EXAMPLES

The present invention will be described further specifically by thefollowing Examples. However, the present invention is in no way limitedto the examples. In the Examples, “parts” are based upon weight unlessotherwise indicated.

Example 1

The buffing composition of this Example was made by mixing 100 parts ofion-exchange water, 2 parts of polycarboxylate (commercially availableunder the trades designation “Carbopol” from BF Goodrich Co., Ltd.), 1part of triethanolamine, 5 parts of diacetone alcohol, and 30 parts ofaluminum oxide particles having an average particle size of 5 μm, andstirring the mixture to form a uniform dispersion with a high shearmixer.

Example 2

The buffing composition of this Example was made according to theprocedure used in Example 1, except that diacetone alcohol was replacedwith propylene glycol monomethyl ether.

Example 3

The buffing composition of this Example was made according to theprocedure used in Example 3, except that 1 part of hydrophilicaminosilicone (a block copolymer of polyether and amino-denaturedsilicone commercially available under the trade designation“NUC-SILICONE” from Nippon Unicar Co., Ltd.), was also added.

Example 4

The buffing composition of this Example was made according to theprocedure used in Example 3, except that hydrophilic aminosilicone wasreplaced with a hydrogenated castor oil (commercially available underthe trade designation “EMULSION A OIL” from CASCHEM Co., Ltd.).

Example 5

The buffing composition of this Example was made according to theprocedure used in Example 3, except that hydrophilic aminosilicone wasreplaced with glycerol.

Example 6

The buffing composition of this Example was made according to theprocedure used in Example 1, except that diacetone alcohol was replacedwith propylene glycol monoethyl ether acetate.

Example 7

The buffing composition of this Example was made according to theprocedure used in Example 1, except that diacetone alcohol was replacedwith acetylacetone.

Example 8

The buffing composition of this Example was made according to theprocedure used in Example 1, except that diacetone alcohol was replacedwith ethylene glycol monomethyl ether acetate.

Example 9

The buffing composition of this Example was made according to theprocedure used in Example 1, except that diacetone alcohol was replacedwith ethylene glycol monomethyl ether.

Example 10

The buffing composition of this Example was made according to theprocedure used in Example 1, except that diacetone alcohol was replacedwith dipropylene glycol monomethyl ether.

Example 11

The lustering composition of this Example was made by mixing 100 partsof ion-exchange water, 5 parts of propylene glycol monomethyl ether, and1 part of hydrophilic aminosilicone, and stirring the mixture to form auniform dispersion with a high shear mixer. Comparative Example 1

The buffing composition of this Example was made by mixing 100 parts ofion-exchange water, 2 parts of polycarboxylate (commercially availableunder the trade designation “CARBOPOL” from BF Goodrich Co., Ltd.), 1part of triethanolamine, and 30 parts of aluminum oxide particles havingan average particle size of 5 μm, and stirring the mixture to form auniform dispersion with a high shear mixer.

Comparative Example 2

A buffing composition commercially available under the trade designation“ULTRA FINISH” from Minnesota Mining and Manufacturing Company was used.This buffing composition contains an oleophilic component.

Performance Evaluation

The buffing compositions of Examples and Comparative Examples were leftto stand at 50° C. for 7 days for observation by eye of presence orabsence of separation and evaluation of stability of the compositionswith the passage of time. The results are shown in Table 1 and Table 2.

The coat surface of a metal test panel painted with a black-coloredhydrophilic coat was sanded using a grade 1500 sanding disc(commercially available under the trade designation “FINESSE-IT MICROFINE” from Minnesota Mining and Manufacturing Company) attached to ahand sanding pad (commercially available under the trade designation“FINESSE-IT” from Minnesota Mining and Manufacturing Company). Thesanding was done with a circular motion and approximately four drops ofwater were added to the sanding interface as a lubricant. The sandingstep formed round scratches having a diameter of about 4 cm on the coatsurface. The average roughness (Ra) of the scratches was about 0.15 μmover the entire surface of the area where the scratches were formed.Then, the painted panel was wiped dry with a cotton cloth.

Next, the prepared buffing composition was applied as a liquid drophaving a diameter of about 1.5 cm to the sanded area. A buffing pad anda finishing pad, (commercially available under the trade designations“FINESSE-IT” and “FINESSE-If ROLOC”, available from Minnesota Mining andManufacturing Company) were secured to a rotary sander buffing tool.

The buffing pad was placed on top of the coat surface to which thebuffing composition had been applied, and the finishing material wasspread over this area before the buffing tool was started. The buffingtool was turned on and the sanded area was buffed for eight seconds asvery firm pressure was applied to the tool. After the eight secondperiod, the pressure was reduced, and it was buffed for additional threeseconds.

Thereafter, the buffing composition remaining on the polished surfacewas washed with water and the polished surface was dried.

Then, the polished surface was lustered by using the lusteringcomposition prepared in Example 11. The lustering composition of Example11 was applied to a surface of coating which had been repaired by thebuffing composition of Example 2, and the surface was buffed in themanner described above.

The polishing performance of each buffing composition, the finish of thecoat surface, hydrophilicity, and stain resistance were evaluated. Theresults are reported in Table 1 and Table 2.

Buffing Performance:

If the scratches formed on the coat surface completely disappeared onthe coat surface after repairing and lustering, it was rated as “o”; ifthey remained only faintly, it was rated as “Δ”; and if they remainedconspicuously, it was rated as “x”.

Finish

The 20° gloss of the polished surface was measured.

Hydrophilicity

Water was applied to the coat surface with a hand spray after repairingand lustering for observation of the state of adhering water. If theentire surface was wetted, it was judged that the hydrophilicity was“present”. If water drops were formed, it was judged that thehydrophilicity was “absent”.

Stain Resistance:

A test piece having a surface of coating which had been repaired andlustered was positioned horizontally. Onto the surface was sprinkleduniformly the 15 kinds of test dust defined in JIS Z 8901 (72% Kantohloam, 23% carbon black, 5% cotton linter) thereafter, using a sieve. Thetest piece was placed in a high temperature oven at 50° C for 2 hours.It was removed from the oven and was left at room temperature for 1hour.

The test piece was raised horizontally, and dropped slightly to pulldown the test dust. The test piece was silently dipped in a water bathfor 1 minute, and took out. Excessive water was wiped by using filterpaper, and the test piece was left at room temperature for 1 hour.

Stain level of the surface of coating was evaluated visually. If thestain was came off, it was evaluated as “o”. If the stain was stayed in,it was evaluated as “x”.

TABLE 1 Example 1 2 3 4 5 6 7 Composition Ion-exchange water 100 100 100100 100 100 100 polycarboxylate 2 2 2 2 2 2 2 triethanolamine 1 1 1 1 11 1 aluminum oxide 30 30 30 30 30 30 30 propylene glycol 5 monoethylether acetate acetylacetone 5 diacetone alcohol 5 ethylene glycolmonomethyl ether acetate propylene glycol 5 5 5 5 monomethyl etherethylene glycol monomethyl ether dipropylene glycol monomethyl etherhydrophilic 1 aminosilicone hydrogenated castor oil 1 glycerol 1Evaluation Presence or absence of Absent Absent Absent Absent AbsentPresent Present separation Buffing performance ∘ ∘ ∘ ∘ ∘ x ∘ Finish 78.578.1 82.5 81.0 78.4 68.2 69.7 Hydrophilicity Present Present PresentPresent Present Present Present Stain resistance ∘ ∘ ∘ ∘ ∘ ∘ ∘

TABLE 2 Comparative Example Example 8 9 10 11 1 2 Compositionion-exchange water 100 100 100 100 100 Conventional productpolycarboxylate 2 2 2 2 “Ultra Finish” triethanolamine 1 1 1 1manufactured by 3M aluminum oxide 30 30 30 30 and containing anpropylene glycol oleophilic component monoethyl ether acetateacetylacetone diacetone alcohol ethylene glycol 5 monomethyl etheracetate propylene glycol 5 monomethyl ether ethylene glycol 5 monomethylether dipropylene glycol 5 monomethyl ether hydrophilic 1 aminosiliconehydrogenated castor oil glycerol Evaluation Presence or absence ofPresent Absent Absent — Absent Absent separation Buffing performance Δ xx — x Δ Finish 58.2 51.4 58.7 82.8 57.7 82.3 Hydrophilicity PresentPresent Present Present Present Absent Stain resistance ∘ ∘ ∘ ∘ x x

The surface of coating which had been repaired and lustered by using thecomposition of Example was hydrophilic, and was superior in stainresistance by comparison with that of Comparative Example.

What is claimed is:
 1. A method for repairing and lustering defects on ahydrophilic coat surface, comprising the steps of: (a) applying abuffing composition on a hydrophilic coat surface, said buffingcomposition comprising: water; a water-soluble high-boiling-point liquidorganic compound having a carbon number of 3 to 12; and either (i) acombination of abrasive particles and a dispersant; (ii) a lusteringagent, or both (I) and (ii); and (b) buffing the hydrophilic coatsurface to which the buffing composition has been applied, wherein thewater-soluble high-boiling-point liquid organic compound is not driedduring the buffing step.
 2. The method according to claim 1, whereinsaid buffing composition comprises relative to 100 parts by weight ofwater: (a) 1 to 50 parts by weight of the water-solublehigh-boiling-point liquid organic compound; (b) not more than 60 partsby weight of the abrasive particles; and (c) 0.5 to 5 parts by weight ofthe dispersant.
 3. The method according to claim 1, wherein said buffingcomposition comprises with respect to 100 parts by weight of water: (a)1 to 50 parts by weight of the water-soluble high-boiling-point liquidorganic compound; and (b) 0.5 to 10 parts by weight of the lusteringagent.
 4. The method according to claim 1, wherein said buffingcomposition comprises with respect to 100 parts by weight of water: (a)1 to 50 parts by weight of the water-soluble high-boiling-point liquidorganic compound; (b) not more than 60 parts by weight of the abrasiveparticles; (c) 0.5 to 5 parts by weight of the dispersant; and (d) 0.5to 10 parts by weight of the lustering agent.
 5. The method according toclaim 1, wherein said water-soluble high-boiling-point liquid organiccompound is selected from the group consisting of polyhydric alcoholshaving a carbon number of 3 to 12, hydroxyketones having a carbon numberof 3 to 12, and ether or ester derivatives of polyhydric alcohols, theester derivatives having a carbon number of 3 to
 12. 6. The methodaccording to claim 1, wherein said water-soluble high-boiling-pointliquid organic compound is diacetone alcohol or propylene glycolmonomethyl ether.